The invention relates to a magneto-optical memory having a substrate of a material which is transparent for the visible to infrared spectral range and on which, there are provided, in the following sequence, a dielectric layer which is transparent for the visible-to-infrared spectral range and has a refractive index which is higher than the refractive index of the substrate and constitutes a diffusion barrier layer for oxygen and/or water, an essentially amorphous and/or essentially micro-crystalline magneto-optical layer with uni-axial anisotropy and a magnetic ordering temperature&gt;ambient temperature and a top layer acting as a reflection or interference layer and as a diffusion barrier layer for oxygen and/or water. The invention also relates to a method of producing such a memory.
In erasable magneto-optical memories writing, reading and erasing information can be effected by means of a localized electro-magnetic radiation.
Reading information from the memory is effected by utilizing either the magneto-optical Kerr effect in reflection or the Faraday effect in transmission.
An erasable magneto-optical memory of an essentially amorphous and/or essentially micro-crystalline magneto-optical storage material is disclosed in, for example, DE-PS 23 40 475.
The object of the dielectric layer is to increase the Kerr effect of the magneto-optical memory and to optimize the write, read and erase behaviour of the magneto-optical memory.
For an optimization of the read efficiency it is effective to provide above the magneto-optical layer a layer which acts either as a reflection or an interference layer, the top layer.
In addition, all the layers contiguous to the magneto-optical layer have the further function of protecting the magneto-optical layer from environmental influences, for example oxidation or corrosion, which might affect the length of operational life of a memory.
If a substrate made of a plastics material, for example polycarbonate, is used, the properties of the dielectric layer must satisfy specific requirements. Depositing the dielectric layer may only be effected at a comparatively low temperature (&lt;80.degree. C.), as otherwise the substrate might be negatively affected. There is however a disadvantage, namely that layers provided on the plastics substrate adhere poorly. The dielectric layer must be mechanically loadable, that is to say it must be elastic, so that it can compensate for internal stresses in the magneto-optical layer provided thereon and when the elastic substrate is distorted it does not crack or chip. The dielectric layer which constitutes a passivation layer for the magneto-optical layer must be chemically stable and must not react with the material of the magneto-optical layer. The optical properties of the dielectric layer must be such that at a wavelength of 800 nm, the operating range of a laser cooperating with the magneto-optical memory, it has a refractive index in the range from 1.9 to 2.5, it being necessary for the absorption at this wavelength to be low (absorption coefficient k&lt;0.05).
The combination of all the required properties is not met by the materials mentioned in the foregoing such as, for example, AlN, SiO.sub.2, CeO.sub.2, Al.sub.2 O.sub.3, used for the dielectric layers. When oxygen-containing materials are used for the dielectric layer there is a risk that the properties of the magneto-optical layer in contact with it will change, for example due to diffusion processes, and is negatively affected. In addition, SiO.sub.2 has a refractive index which is too low for such a use. Dielectric layers made of all the above-mentioned materials have furthermore too low a ductile yield, so that on mechanical loading of a comparatively elastic substrate they crack or chip and consequently can no longer perform their function as passivating layers.